1. Field of The Invention
The present invention is related to an arrangement of printed circuit traces, and more particularly to an arrangement of printed circuit traces which ensures proper signal transmission by eliminating cross talk between adjacent signal traces.
2. The Prior Art
Printed circuit boards are essential elements of any computer system for mounting electrical components thereon and providing an efficient method of signal transmission between the components through signal traces formed therein. Flexible printed circuits are also becoming increasingly popular due to the efficient use of space provided thereby. As the trend of the computer industry continues toward miniaturization, the signal traces of printed circuits are being formed at increasingly higher densities. Such close proximity results in cross talk between adjacent signal traces which adversely affects signal transmission.
A conventional arrangement of printed circuit traces is shown in FIG. 5. A ground plane 25 is formed on a bottom surface of a substrate 30 and a plurality of signal traces 10 are formed on a top surface thereof. Since the signal traces 10 are formed adjacent to each other near one surface of the substrate, cross talk therebetween and, subsequently, poor signal transmission are inevitable. In addition, control of the effective impedance of the signal traces 10 and ground plane 25 becomes complicated since the only variable design parameters are the depth and width of the signal traces 10. An increase in the width of the signal traces 10 would result in more cross talk therebetween, and an increase in the height of the signal traces 10 would increase the occupied space of a circuit board in which the signal traces 10 are formed.
FIG. 6 shows a conventional four layer printed circuit arrangement used in high speed signal transmission applications. A pair of internal planes 25, 45 serve as a means for conducting ground and power signals, respectively, and a substrate 30 is provided therebetween and on outer surfaces thereof. Signal traces 10 are formed on near outer surfaces of the substrate 30. Cross talk between adjacent signal traces 10 is reduced by such an arrangement but the cost of manufacture is greatly increased. Furthermore, control of the effective inductance between power and ground becomes complicated due to the power and ground planes 25, 45 not having variable parameters.
Therefore, an improved arrangement of printed circuit traces is required which can overcome the disadvantages of the prior art.